Jan Tammes (Tammens), a Dutch Mennonite (Old Flemish), probably a preacher, in the town of Groningen, who was excommunicated in 1688 because of his Collegiant sympathies and his view that baptism must be by immersion. He held somewhat advanced ideas and could not believe that the Groningen Old Flemish branch was the only true Christian church. He defended Christoffel Wensing when Wensing joined the Collegiants. His followers were called the Jan-Tammesvolk.